Brake test benches serve to test, in particular, vehicle brakes, for example, with regard to wear and tear, coefficient of friction, noise emission, fatigue strength, power, etc. For this purpose, the brake to be tested is connected to the test bench. Therein, it is, on one hand, possible to install the brake in the test bench as an independent component and to connect it to the test bench components there. On the other hand, it is also possible to install a complete vehicle or even parts of the vehicle (axle components, etc.) in the test bench and then to connect the brake to be tested to the test bench. The brake, on its part, is driven and/or loaded by a dynamometer on the test bench side in known manner.
In all of these cases, the brake pressure required for actuating the brake is generated and provided by the test bench. The only item forming the unit under test is the actual brake, which, e.g., substantially comprises a brake disk and a caliper carrying the brake pads and brake pistons. The test bench generates the brake pressure and provides the brake fluid with an appropriate brake pressure.
In line therewith, a pressure generating assembly is provided in the test bench, the pressure generating assembly comprising a brake master cylinder. The brake master cylinder is to be actuated in the same manner as the brake master cylinder in a vehicle. In line therewith, the brake master cylinder of the test bench must be actuated in the same manner as the brake master cylinder in a vehicle in order to test the brake as closely to reality as possible. For this reason, to be able to test a vehicle brake that is actuated hydraulically, a vehicle driver's braking foot must be simulated on the test bench. It is known to provide an actuator for generating the pressure, e.g. simulating the braking foot and, therefore, actuating the brake system.
As a general rule, the brakes of passenger vehicles and light trucks are actuated hydraulically. To be able to operate these brake systems in test benches through an actuator, both the reachable (maximum) pressure and the pressure gradients (rate of building up the pressure) must be reached at least as well as in a real vehicle. This means that the actuator must build up a brake pressure of at least 250 bar with a pressure gradient of at least 200 bar per second. In line therewith, considerable power requirements must be met by the actuator.
In the past, various systems were used on test benches for the actuator to simulate the driver's foot and, therefore, to apply the pedal force when the brake is actuated. For example, there exist what are referred to as pneumatic/hydraulic transformers in which the brake actuator for generating the pedal force and, therefore, for actuating the brake master cylinder is operated pneumatically (pneumatic primary circuit) whereas the actual braking circuit (secondary circuit) is configured hydraulically (hydraulic brake system). Likewise, there exist hydraulic/hydraulic systems in which the actuator in the primary circuit is driven hydraulically as well. Therein, a pressure is generated in the primary circuit through a hydraulic pump and the pressure is transmitted to the secondary circuit (vehicle brake system) with the brake fluid through a valve and a hydraulic master cylinder, this being achieved through an actuation rod.
In these systems, considerable complexity in terms of construction (special valves, friction-reduced and force-lubricated cylinders) is required to achieve particularly the dynamics mentioned above (high pressure gradient).
A two-station gyrating mass brake test bench is disclosed in German Patent DE 101 23 828 C1, in which the driver's foot is simulated by an actuator. Therein, the complete brake system of a vehicle, including the brake master cylinder of the vehicle, is tested. A controllable electric drive with spindle drive can be used as an actuator.
Furthermore, so-called brake assists are known, which additionally support the build-up of pressure in the brake system through an electrically driven auxiliary actuator. In case of an emergency brake application, the braking force the driver applies through the brake pedal can, therefore, be supported by the auxiliary actuator. A corresponding example is shown in European Patent Application EP 2 100 784 A1 corresponding to U.S. Pat. No. 7,922,264 to Baumann et al.
Thus, a need exists to overcome the problems with the prior art systems, designs, and processes as discussed above.